There are generally two categories of battery applications: energy storage applications and power applications. For energy storage applications, the battery tends to be discharged quickly and charged back slowly, or vice versa. For such applications the battery capacity is such that the battery's RMS C-rate is typically less than 0.5 C. In many cases, the battery's RMS C-rate is less than 0.1 C. Example energy storage applications include uninterruptible power supply (UPS), and load leveling of solar power to accommodate for gaps between power demand and supply at different times of the day (e.g. day versus night).
In power applications, the battery needs to supply energy within a short time frame, and be quickly recharged to be ready for the next event. Power applications require less energy storage but more power to be delivered. For such applications the battery's RMS C-rate is generally above 0.5 C, and in some cases, approach 10 C. Example power applications include grid frequency regulation and grid stabilization.
As current flows through a battery cell, the cell's internal resistance produces heat. The flow of current I through a cell having a resistance R over a specified time t generates heat Q in accordance with Joule's first law:Q=I2·R·t  Equation (1)wherein the heat Q produced is equal to the square of the current I multiplied by the resistance R of the cell and the time t. As can be seen from Equation (1), increasing the current I from 1 C to 4 C (as may be required for power applications, for example) will increase heat generation by a factor of 16 (i.e. (4 C)2/(1 C)2). Therefore, even for a moderate increase in current, it can become a challenge to remove the heat generated by a battery cell. If the cell overheats, thermal runaway can occur. If the cell is stacked in close proximity to other battery cells, then the thermal runaway in the cell can propagate to these other cells, which may result in a fire or explosion.
Because of the challenges in cooling a cell when increasing the current, manufacturers of large format batteries typically focus their efforts on the design of batteries for energy storage applications where the battery's RMS C-rate is relatively low as discussed above. However, when such batteries are used for power applications, large capacity battery modules are required to meet the power application demands. This leaves extra battery capacity that is not being used much of the time.
Battery cells come in different sizes and shapes, including cylindrical or flat. Due to its geometry, it is generally difficult to remove heat from a cylindrical cell, such as, for example, an 18650 cell (or the like) which is typically about 65 mm long and about 18 mm in diameter and has a capacity of 2 Ah. Instead of cylindrical cells, flat cells are often preferred for high power battery applications, since flat surfaces can be cooled more efficiently. Flat cells include, for example, prismatic cells, layered cells, pouch cells and the like.
Some efforts have been made to address the cooling of multi-cell battery power systems. Methods of cooling battery cells include, for example, passive radiation, air cooling and liquid cooling. For battery power systems incorporating flat cells, methods of cooling include:                Placing the pouch cells in a cell carrier which holds the pouch cells by their edges, and providing cooling passages to cool the edges, as described for example in US Patent Application Publication No. 2013/0266838. This design relies on the thermal conductivity of the battery cell itself to distribute heat to the edges. This may not be effective in cooling the battery cell in high power battery applications since the thermal conductivity of the battery cell is low.        Placing the pouch cells in a plastic cell carrier and placing a heat conductive sheet over each pouch cell to move heat to an outside edge of the plastic cell carrier, as described for example in U.S. Pat. No. 8,835,037. The heat conductive sheet is thin (typically less than 1 mm thick) and thermal conductivity of the heat conductive sheet is typically anisotropic or directionally dependent (for example, a graphite sheet has very high in-plane conductivity but very low through-plane conductivity). Due to these limitations, the battery cell may not be sufficiently cooled in high power applications, and thermal runaway may occur, damaging the plastic cell carrier and the cell.        Placing the pouch cells in an aluminum casted structure that has small liquid-containing channels close to the flat surface of the cells, as described for example in U.S. Pat. No. 8,404,375. This design is subject to various drawbacks: the small liquid channels may not provide for reliable flow; the channels are prone to leaks of the liquid coolant due to the thinness of the channel walls; and the apparatus is complex and therefore difficult and costly to manufacture.        
There is a general desire for apparatus, systems and methods that address and/or ameliorate at least some of the aforementioned problems and otherwise assist with cooling a high power battery cell, module and/or system.
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.